Saitoh disclosed a combination lock in his U.S. Pat. No. 4,445,348 which is capable of being set in any desired combination of numbers or changed from the once set specific combination to any other combination without using any tool. However, when changing the combination to a new one, the outermost dial ring should be first dismounted from the corresponding inner ring and the other dial rings should then be disengaged. After re-setting a new combination, the dial rings should be fitted on the inner rings one by one, causing a very inconvenient operation for changing a new combination.
Mayer et al disclosed a permutation lock in their U.S. Pat. No. 4,354,365. For changing a new combination, the closing bolt 18 should be retracted outwardly to retard an inwardly radial movement of the shank 31 of locking pin 28 so that the inner rings 36 are secured against rotation for re-setting a new combination. However, the retraction of the bolt 18 should be done very carefully. Otherwise, if the recess 32 between every two lands 76 of the bolt 18 is meeting the shank 31, the pin 28 will not be retarded radially outwardly, allowing a coupled rotation of the two rings 36, 38 thereby influencing the operation for changing the combination.
Meanwhile, Mayer's pin head 30 of each locking pin 28 resiliently urges two neighbouring rings commonly for safety purpose. If only one ring (rather than two rings) partially depresses the pin head 30 to lower the pin 28 to be engageable with the recess 32 for locking the bolt 18, the locking pin 28 may be inclinedly biased downwardly deviating from a vertical axis of the pin 28, thereby influencing a smooth downward sliding movement of the pin or increasing a difficult locking operation therefor.
The present inventor has found the drawbacks of the conventional combination locks and invented the present combination lock.